1. Field of the Invention
A novel method of achieving microbiological control in open recirculating cooling water systems comprising ozonation of the recirculating water in combination with addition of elevated levels of bromide salts (method referred to hence forth as OzoBrom).
2. Description of the Prior Art
The prior art teaches that ozone-activated bromine has been used as a biocide in swimming pools. However, no additional treatment chemicals are necessary for swimming pools. As a result, the bromide levels in swimming pool applications are very low.
Rice and Wilkes have recently reviewed the subject of ozone-activated bromine in cooling water systems (R. G. Rice, J. F. Wilkes, "Bromide Ion--Its Possible biocidal Role with Ozone in Cooling Water Treatment", Industrial Water Treatment, 24, 1992, pp 40-48). Although the concept of ozone-activated bromine in cooling water systems is a known technology, no investigations have been performed in the presence of scale and corrosion control treatment chemicals. The prior art teaches that bromide concentrations of 2-15 ppm are sufficient for proper control. The prior art also teaches that at these bromide concentrations the ozone oxidizes much of the organic material present in the system. Since most corrosion and scale control treatment chemicals are organic, a problem exists in trying to balance the competing interest of scale and corrosion control versus microbial growth control.
Ozone-activated bromine serves as a microbiocide in open recirculating cooling water systems. Existing products used for microbial control in cooling water systems include chlorine, bleach, BCDMH (bromochlorodimethyl hydantoin) or combinations thereof (e.g. chlorine-activated bromine). These products have hazards associated with their transportation, handling and feeding. The in situ production of bromine by ozone eliminates these hazards. Further, reaction of existing microbial control products with small organic molecules can result in the formation of undesirable trihalomethanes (THM). Exposure of the recirculating water to ozone can result in destruction of THM precursors, thus reducing the production of the undesirable by-products.
Strittmatter has shown that ozone destroys most organic-based cooling water treatment chemicals, resulting in improper corrosion and scale control (R. J. Strittmatter, CORROSION/93, Paper #477, NACE: Houston, Tex.). Therefore, it is necessary to prevent oxidation of these treatment chemicals in open recirculating cooling water systems.